Digital Subscriber Line (DSL) communications suffer from various forms of interference, including crosstalk. Various techniques have been developed to combat this interference and its effects on data transmission, including vectored DSL. The amount of vectoring-related data that must be transmitted between downstream and upstream modems is substantial for vectored DSL systems; vectoring data relating to crosstalk also must be stored, updated, manipulated and/or processed by upstream devices such as vectoring control entities and/or other vectoring modules.
Vectoring mitigates crosstalk inherent in twisted-pair DSL networks by cancelling or pre-cancelling crosstalk (i.e. FEXT) interference in the signals of a vectored group of co-located transceivers. The crosstalk from and into every transceiver is described as a matrix (channel matrix) for every tone (frequency) used by the individual transceivers. To perform cancellation, the vector processing system must have access to the signals from and to each transceiver participating in a vectored group, and cancellation information is embodied in coefficients that describe the inverse (or approximate inverse) of the channel matrix. Because the number of coefficients increases as the square of the number of DSL lines in a vectored group, and because earlier systems have stored coefficients for each unit and frequency as fixed size numbers, memory requirements in vectored systems increase rapidly with larger vectored groups.
Certain conventional approaches for addressing these demands in vectored systems exist. One approach is called partial cancellation. Partial cancellation techniques include line selection (i.e. retaining coefficients for only the dominant disturber DSL lines) and tone selection (i.e. retaining coefficients for only the dominant disturbing tones), but both of these methods require supervision (e.g., supervising software, firmware) to monitor tones and/or lines being cancelled. Since network characteristics and operating conditions change over time, these monitoring functions must be maintained as the conditions change. Moreover, partial cancellation, by definition, causes performance on non-cancelled channels to suffer.
Commonly owned application Ser. Nos. 13/002,213 and 13/189,095, the contents of which are incorporated herein by reference in their entireties, describe various useful and valuable techniques for reducing memory, transfer and processing demands on a vectored DSL system, and which can be implemented to manage precoder coefficients for all available victims, disturbers and tones (i.e. nodescale vectoring). However, opportunities for further improvement remain.